Soybean, Glycine max (L.) Merril, is a major economic crop worldwide and is a primary source of vegetable oil and protein (Sinclair and Backman, Compendium of Soybean Diseases, 3rd Ed. APS Press, St. Paul, Minn., p. 106, (1989)). The growing demand for low cholesterol and high fiber diets has also increased soybean's importance as a health food.
Soybean varieties grown in the United States have a narrow genetic base. Six introductions, ‘Mandarin,’ ‘Manchu,’ ‘Mandarin’ (Ottawa), “Richland,’ ‘AK’ (Harrow), and ‘Mukden,’ contributed nearly 70% of the germplasm represented in 136 cultivar releases. To date, modern day cultivars can be traced back from these six soybean strains from China. In a study conducted by Cox et al., Crop Sci. 25:529-532 (1988), the soybean germplasm is comprised of 90% adapted materials, 9% unadapted, and only 1% from exotic species. The genetic base of cultivated soybean could be widened through exotic species. In addition, exotic species may possess such key traits as disease, stress, and insect resistance.
Soybean stem canker is caused by Diaporthe phaseolorum sp. and results in reductions in yield.
There is a need in the art of plant breeding to identify additional markers linked to quantitative trait loci associated with stem canker resistance in soybean. There is in particular a need for numerous markers that are closely associated with stem canker resistance QTLs in soybean that permit introgression of the stem canker resistance QTL in the absence of extraneous linked DNA from the source germplasm containing the QTL. Additionally, there is a need for rapid, cost-efficient method to assay the absence or presence of stem canker resistance loci in soybean.